Imaging system utilizing spatial coding

ABSTRACT

An imaging system suitable for use with high energy nuclear particles or photons such as gamma radiation and X-radiation. The system provides means for illuminating an object with radiation as well as spatially coding the illuminating radiation or emitted radiation if the object is self-luminous, to provide a composite image representing the summation of the shadows from all points of the source of illumination. Spatial modulation is accomplished by a mask having a coded pattern of transparent and opaque regions linearly scanned in time. The resulting signal has the characteristics of a chirp waveform typical of pulse compression radars. The composite image is readily decoded by a delay line having a phase or delay characteristic complementary to that of the spatial modulation pattern.

United States Patent [1 1 Barrett IMAGING SYSTEM UTILIZING SPATIALCODING [75] Inventor: Hal-r1365nisaracteimgian,

Mass.

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Mass.

[22] Filed: Oct. 2, 1970 [211 App]. No.: 77,459

[52] U.S. Cl .[l250/363I256/l65 [51] Int. Cl. G0lt 1/20 [58] Field 01Search 250/7l.5 S, 105

[56] References Cited UNITED STATES PATENTS 3,509,341 I 4/1970 Hindcl etal 250/715 S 3,573,458 4/1971 Anger 250/715 S FOREIGN PATENTS ORAPPLICATIONS 42,595 12/1965 Germany 250/105 DETECTOR [451 July 24, 1973Primary Examiner-Archie R. Borchelt Attorney-Milton D. Bartlett, JosephD. Pannone, Herbert W. Arnold and David M. Warren [57] ABSTRACT Animaging system suitable for use with high energy nuclear particles orphotons such as gamma radiation and X-radiation. The system providesmeans for illuminating an object with radiation as well as spatiallycoding the illuminating radiation or emitted radiation if the object isself-luminous, to provide a composite image representing the summationof the shadows from all points of the source of illumination. Spatialmodulation is accomplished by a mask having a coded pattern oftransparent and opaque regions linearly scanned in time. The resultingsignal has the characteristics of a chirp waveform typical of pulsecompression radars. The composite image is readily decoded by a delayline having a phase or delay characteristic complementary to that of thespatial modulation pattern.

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IMAGING SYSTEM UTILIZING SPATIAL CODING BACKGROUND OF THE INVENTION Thisinvention pertains to the focusing of radiant en ergy and, moreparticularly, to radiation characterized by the presence of high energyparticles, particularly high energy photons such as in gamma radiation.

In the past, focusing of radiation has been done by lenses where theradiation is of a lower frequency, such as optical radiation, and bymeans of pinhole cameras or collimator arrays where the radiation if ofa higher energy, such as gamma radiation. The pinhole camera has beenutilized because the index of refraction at all materials is too smallto permit lens construction.

One well-known type of camera for use with gamma radiation imaged by apinhole or parallel hole collimator array is the Anger camera asdisclosed in US. Pat. No. 3,0] 1,057, which issued to H. O. Anger onNov. 28, I961. While such a camera is in common usage today, itsperformance is inferior to that of cameras customarily used for opticalradiation in that its resolution is substantially lower and itseffective aperture, no larger than a pinhole, is far smaller than thatof the wide aperture lenses commonly employed in optical cameras todayand can be increased at the expense of resolution. Thus, there is aproblem as to how to construct a system responsive to high energyradiation which provides real-time imaging of extended objects, such asmight appear on a television screen, and variable focusing, for the casewhere the object-to-camera distance is variable.

SUMMARY OF THE INVENTION This invention provides wherein an objectemitting, or illuminated by, high energy radiation, such as X-radiation, gamma radiation, and nuclear radiation, is observed or imagedby spatially coding the illumination so that there is received acomposite image having shaded regions, the shading being due to both theshadows cast by the object itself as well as shadows due to the spatialmodulation of the radiation. The shading is the variation over the imageplane in the probability of arrival of high energy photons. In oneembodiment of the invention, the spatial modulation of the radiation isaccomplished by means of a mask or plate having regions which aretransparent and regions which are opaque to the radiation. The opaqueregions may be regarded as barrier elements which inhibit the passage ofparticles suchas gamma ray photons and nuclear particles. The inventionis particularly useful where the dimensions of the transparent andopaque regions of such marks are, in practical devices, much larger thana wavelength of the radiation which precludes the use of interference ordiffraction effects to alter the direction of a ray. In a secondembodiment of the invention, the spatial modulation of the radiation isaccomplished by illuminating the object by means of a source ofradiation comprising emitting areas from which high energy particlesemanate which are intespersed among nonemitting areas from which no highenergy particles emanate. With both embodiments, the pattern ofilluminated and shaded areas has a code or predetermined format.

A detector assembly is positioned to intercept the radiant energy whichin the case of gamma radiation comprises a sequence of photons, orquanta of radiant energy. An image of these rays is formed on the faceof the detector assembly, the image being scrambled due to the spatialmodulation. An image of the object itself is provided by scanning thescrambled image on the face of the detector assembly to provide a scansignal containing information relating to the locations of the variousportions of the scrambled image. The scan signal is passed through afilter having a transfer function which is conjugate to the scan signalproduced from a point source of radiation through the spatially codedmask, that is, the temporal impulse response function of the filter isthe temporal inverse of the scan signal waveform, so that there is acorrelation between the filter and the spatial modulation. Thus, forexample, where the modulating elements have the form of a series ofopaque and transparent regions of successively decreasing size, the scansignal has a form similar to that of a chirped radar signal where thefrequency is linearly increasing; and accordingly, in this case thefilter would have the form of a pulse compression filter providingdifferential delays between portions of the signal having differingfrequencies. Thus, the image of the radiant energy on the face of thedetector assembly would be decoded and compressed into a series ofpoints which are then displayed as the image of the object.

BRIEF DESCRIPTION OF THE DRAWINGS The aforementioned objects and otherfeatures of the invention are explained in the following descriptiontaken in connection with the accompanying drawings wherein:

FIG. 1 is a pictorial representation of a system in accordance with theinvention for displaying a radiograph of a radioactive object;

FIG. 2 is a block diagram of the imaging system of the invention;

FIG. 3 is a pictorial view of a mask used in the invention;

FIG. 4 is a pictorial view of an alternative embodiment of the maskutilized in the invention;

FIG. 5 is a plane view of a dispersive surface wave delay line showing avariation in the spacing of fingers in a comb structure;

FIG. 6 is a plane view of a portion of a surface wave delay line showinga variation in the overlapping of the fingers in an interdigitalnetwork;

FIG. 7 is an alternative embodiment of the imaging system of theinvention;

FIG. 8 is a further embodiment of the invention wherein a large spatialfrequency bandwidth is provided by a source of radiation;

FIG. 9 is a detailed view of a source of radiation providing a largespatial bandwidth in accordance with the invention;

FIG. 10 is a diagrammatic view of a radiographic system employingspatial filtering of an image formed with the aid of the source of FIG.9; and

FIGS. 11 and 12 are diagrammatic views of alternative embodimentsshowing a mechanical scanner and an image intensifier.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1 there isshown a human patient 20 being treated for a thyroid ailment with theaid of equipment responsive to gamma radiation. As is well known, thethyroid gland tends to absorb compounds of iodine which may be injectedinto the patient or ingested by the patient. To provide a radiograph ofathyroid 21 a radio pharmaceutical containing iodine is administered tothe patient. The radioactive molecules of the radiopharmaceutical arethen distributed about the thyroid gland and emit gamma radiation, thegamma radiation from each of the molecules forming a part of theradiograph.

In accordance with the invention a radiograph is formed by means of animaging system 22 comprising a detector assembly 24 responsive to gammaradiation, a processor 26 for deriving information from each of the highenergy photons of the gamma radiation as they impinge on the detectorassembly 24, and an output display 28 for showing a radiograph of thethyroid 21. In addition, a mask 30 having an array of apertures ofpredetermined sizes, indicated generally by the numeral 32, which arearranged in a predetermined manner as will be shown in greater detailhereinafter with reference to FIGS. 3 and 4, is utilized instead of thepinhole aperture or collimator array commonly used for photography ofhigh energy particles. The mask 30 creates a scrambled or coded image atthe face of the detector assembly 24 as will be described hereinafterwith reference to FIG. 2, and accordingly, the processor 26 incorporatesmeans for decoding the scrambled edge. The mask 30 serves the dualfunctions of providing increased aperture and permitting a higherresolution than has hithertofore been possible with such largeapertures. The larger aperture admits high energy gamma ray photons at arate far greater than possible with a single pinhole aperture orcollimator and thereby reduces the time required to make a radiograph.

Referring now to FIG. 2 there is shown a block diagram of the imagingsystem 22 of the invention in which an object 34 such as the radioactivethyroid 21 emits radiation in the direction of the mask 30 and detectorassembly 24. The detector assembly 24 has a form similar to that of theAnger camera as disclosed in the aforementioned patent to Anger andutilizes a scintillator 36, such as cesium iodide crystal in the form ofa plate, which is illuminated by radiation shown as rays SSA-D from theobject 34. As is well known, a scintillator emits light from the pointof impact of a high energy particle which may be a high energy photonfrom gamma radiation or X-radiation as well as an impact from a nuclearparticle such as a proton or a neutron. An array of detector elements 40are arranged to intercept the light, for example the light rays 42emitted from the sites of such impacts on the scintillator 36. Asdisclosed in the aforementioned patent to Anger the detector elements 40are connected to a matrix 44 of resistors which provide the X and Ycoordinates. Currents are induced in the resistors (not shown)proportional to the intensity of the light received at the respectivedetector elements 40. Since the intensity of light impinging upon anyone of the detector elements 40 is related to the angle of arrival ofthe light rays 42 from a point of impact on the scintillator 36 to adetector element 40, the currents in the resistor matrix 44 are relatedto the location of the point of impact on the scintillator 36. Thus, theresistor matrix 44 is able to provide the X and Y coordinates of theimpact location as shown on lines 46 and 48. Since the detector assembly24 is responsive to nuclear particles as well as high energy photons,the imaging system 22 can form a radiograph of an object radiating highenergy in the form of nuclear particles as well as high energy photons.

The operation of the imaging system 22 is readily distinguished fromwell known optical imaging systems which commonly employ reflectingsurfaces or lenses to produce images. In the case of a lens used in suchoptical systems the index of refraction of the material used in the lensvaries with frequency and approaches unity for the higher radiationfrequencies as are found in X-radiation and gamma radiation as well asfor nuclear particles. Thus, in high energy radiation imaging systemsthe use of optical lenses is precluded in that there is insufficientindex of refraction to bend the rays of radiation to form an image. Andsimilarly with the reflecting surfaces of mirrors used in opticalsystems, at the higher energy radiation, such as X-radiation andparticularly gamma radiation and nuclear radiation, the reflectingsurfaces tend to be no longer reflecting and such radiation proceeds totravel straight through the material used in the reflecting surface.

The mask 30 and the detector assembly 24 do not use the focusing effectassociated wit the bending of rays of radiation as is done in thetypical optical system. The image formed on the scintillator 36 isproduced by techniques of geometric optics analogous to that of thepinhole camera in which all rays of radiation are straight. Accordingly,the operation of the mask 30 is to be distinguished from that ofdefraction gratings in optical systems of the prior art.

The operation of the mask 30 can be explained as follows. Consider apoint source such as source 50 of high energy radiation located on theobject 34. The source 50 emits quanta of radiation, either a photon ornuclear particle, which travls from the object 34 to the mask 30. Thequanta of energy passes through the mask 30 in the event that it isemitted in a direction towards an aperture 32, or is stopped by the mask30 in the event that it is emitted in a direction towards an opaquesection of the mask. The source 50 emits the quanta of energysequentially and at irregular intervals. If the scintillator 36 were tohave a very long persistence time compared to the mean interval betweenthe emitted quanta of radiant energy then it would be observed that animage or shadow of the mask 30 would gradually appear on thescintillator 36 as successive quanta of radiation passed through theapertures 32 to impact upon the scintillator 36.

As a practical matter, cesium iodide scintillators do not havesufficient persistence time for forming an image when illuminated by anobject such as the radioactive thyroid 21. Accordingly, the X-Ycoordinate position data of each of the impact points must be processedin a manner which preserves the data of the individual impact pointsuntil such time as there are a sufficient number of these points toprovdie a usable image. Thus, for example, the X-Y coordinate data onlines 46 and 48 could be processed by a computer (not shown) whichprovides a memory address code for each of the impact points, or as isshown in the preferred embodiment of FIG. 2 the processor 26 utilizes afirst storage tube display 52 responsive to the X-Y coordinate data onlines 46 and 48. The first storage tube display 52 has a cathode raytube (not shown) with a long persistence storage screen, hereinafterreferred to as the first storage screen 54, which as is well known,emits light in response to the impact of electrons from the electron gunof the cathode ray tube. The details of the first storage tube display52 are not shown since they are well known. The first storage tubedisplay 52 additionally contains a circuit responsive to the presence ofthe electrical signals on lines 46 and 48 for energizing the beam of thecathode ray tube to illuminate the first storage screen 54 at the pointcorresponding to the X and Y coordinates. In this way the sequentialimpact of quanta of radiant energy from the source 50 upon thescintillator 36 are transformed into an image on the first storagescreen 54, the image having the form of the shadow of the maskcorresponding to illumination of the mask 30 from the point source 50.Since a radioactive object such as the radioactive thyroid 21 has manypoints which serve as sources of radiation, each such point being asmall volume of radioactive material, a multiplicity of images areformed and superposed on the first storage screen 54 in response toillumination of the mask by each of these sources such as the sources50, 56 and 58. It is thus apparent that the image appearing on the firststorage screen 54 is in fact a scrambled or coded image of the object 34since it bears little, if any, resemblance to the object 34 and yetcontains all the information as to form the object 34. The next step informing a radiograph of the object 34 is therefore the unscrambling ordecoding of the image on the first storage screen 54.

The decoding of the scrambled image on the first storage screen 54 canbe done, for example, by a computer (not shown) which processes the X-Ycoordinate data in accordance with programs utilizing the mathematics ofconvolution and Fourier transform operations, or as is shown in thepreferred embodiment of FIG. 2, by means of scanning technique whichutilizes the matched filter or pulse compression technique of radarsystems. The processor 26 unscrambles the image in a two-step procedurein which it first unscrambles the image in the horizontal dimension andthen unscrambles the image in the vertical dimension.

The first step in the decoding is accomplished by means of a firstvidicon 60 and a first delay line 62. The first vidicon 60 horizontallyscans the first storage screen 54 and provides an output signalconsisting of successive horizontal line scans. The first vidicon 60utilizes a linear sweep rate when scanning storage tube screens that areflat; a nonlinear sweep rate is utilized for curved storage tube screensin order to cancel the effect of the curvature so that the output signalfrom the first vidicon 60 has the characteristics of a linear scan. Thewaveform of the signal provided by each line scan of the first vidicon60 corresponds to the shadow cast upon the scintillator 36 and isreadily visualized in the case of illumination of the mask 30 by asingle source of high energy radiation such as the source 50.

The shadow cast by the mask upon the scintillator 36 comprises asuccession of light and dark areas as can be visualized by examining theaxonometric view of the mask 30 as shown in FIG. 3 as well as thediagrammatic sectional view taken through a line of apertures 32 asshown by the mask 30 of FIG. 2. The mask 30 comprises an array ofapertures 32 of relatively transparent areas formed within a basematerial such as lead which is relatively opaque to high energyradiation, the opaque portion being designated by numeral 64. Since theopaque portion 64 is a relatively thin film in the case of X-radiationor gamma radiation, the opaque portion 64 is supported by a rigidsubstrate 65 of relatively transparent material such as a material oflow atomic number, for example, aluminum.

In an alternative embodiment of the mask indicated by numeral 66 andshown partially cut away in FIG. 4, apertures 68 do not pass completelythrough the base material so that there is a small amount of opacityeven in the relatively transparent region of the mask 66. The embodimentof FIG. 4 represents one method of reducing the effect of radiationresulting from Compton scattering within the object 34 of FIG. 2 since,as is well known, the radiation resulting from the Compton scattering isof a lower energy than the direct radiation from the soruce 50.Accordingly, the mask 66 shown in FIG. 4 can provide an image on thefirst storage screen 54 having greater definition than does the mask 30of FIG. 3. With either the embodiment of the mask as shown in FIG. 3 orthat shown in FIG. 4 substantially the same shadow pattern is developedby the mask on the scintillator 36 in response to radiation emanatingfrom the source 50.

Referring again to FIGS. 2 and 3 the configuration of the apertures 32and their arrangement may be readily explained by considering anaperture array of one dimension such as the row of apertures 70A-D. Forease of reference in this description of the aperture arrangement, eachof the apertures 32 are further designated by individual numeralsfollowed by letters, the numeral indicating the row position and theletter indicating the column position. The row of apertures 70A-D areconfigured and arranged so that when the image of the row of apertures70A-D on te first storage screen 54 is scanned, a chirp waveform similarto that utilized in a pulse compression radar system appears on theoutput signal on the first vidicon 60.

Recalling that a linear scan is utilized by the first vidicon 60, theoutput signal of the first vidicon 60 has the form of a square wave inwhich the period of the square wave is linearly increasing with time orlinearly decreasing with time. The first delay line 62 to which thesignal is applied is responsive to the repetition frequency of thesquare wave, so that for purpose of this analysis the higher orderharmonics of the square wave can be disregarded. Therefore, the chirpedsquare wave may be regarded as a chirped sine wave having a frequencywhich is linearly increasing with time as the image of the apertures70A-D is scanned in the direction from aperture 70A to aperture 70D, theinstantaneous frequency of the chirped sign wave being linearlydecreasing in time when the image of the apertures 70A-D is scanned inthe direction from aperture 70D toward aperture 70A. As shown in FIG. 3the dimensions of contiguous opaque and transparent regions of the maskdiffer only slightly in the direction of scanning, with the spacingsbetween the respective apertures 70A-D decreasing linearly as do thewidths of the apertures 70A- D.

In the dimension perpendicular to the direction of scanning, which forease of reference may be referred to as the height of the apertures, isuniform form along the row of apertures 70A-D. The height of theapertures in the next row of apertures, namely the height of theapertures 72A-D is also of uniform magnitude along the row of apertures72A-D, but is smaller than the height of the apertures in the row ofapertures 70A-D. The heights of the successive rows of and the spacingsbetween the successive rows decreases linearly so that the height of therow of apertures 74A-D is smaller than that of the row of apertures72A-D, and similarly the height of the row of apertures 76A-D is smallerthan that of the row of apertures 74A-D. In this way a vertical scanningof the image or shadow of the mask 30 results similarly in a chirpedwaveform.

Returning now to FIG. 2 the horizontal scanning of the first storagescreen 54 by the first vidicon 60 results in a chirped waveform for thereasons described hereinabove with reference to FIG. 3. The chirped waveof the first vidicon 60 is applied to the first delay line 62 which isfrequency dispersive and furthermore has a phase or time delaycharacteristic which is the inverse (or the mirror image), of thechirped square wave. Signals of different frequencies experiencedifferent time delays in progressing through the first delay line 62.The first vidicon 60 together with the first delay line 62 may beregarded as a transmission medium through which portions of the image onthe first storage screen 54 are sequentially transmitted, the mediumbeing characterized by a differential delay imparted to the variousportions of the image. As is well known from the theory of matchedfilters and the pulse compression filters utilized in radar systems (forexample, see the article entitled The Theory and Design of Chirp Radarsby JR. Klauder, A.C. Price, 8. Darlington and W. J. Albersheim in theBell System Technical Journal of July 1960, Volume 39, pages 745-808), afilter having an impulse response which is the inverse of the timewaveform of the input signal applied to the filter provides an outputsignal in the form of a narrow pulse. In the case of a wide bandwidthinput signal, such as the chirped waveform of the imaging system 22, theoutput signal of such a filter approximates an impulse. Accordingly, theoutput signal of the first delay line 62, assuming the mask 30 to beilluminated by the single source 50, may be regarded as an impulse whichcorresponds to the position of the source 50. The impulse is displayedon the screen 78 of a second storage tube display 80. The position ofthe displayed impulse on the second storage screen 78 is in response tothe location of'the source 50 relative to the mask 30 and the detectorassembly 24. Thus, the imaging system 22 can show the direction to asource of high energy particles.

If the mask 30 were illuminated by high energy radiation from the source56 which is spaced apart from the source 50, the resulting image on thefirst storage screen 54 would differ from the image obtained byillumination of the mask by source 50. The chirped wave form signalbeing produced by the first vidicon 60 in response to the scanning ofthe image produced by the source 56 differs from that associated withsource 50 in that the occurrence of a particular instantaneous value ofpulse repetition frequency is attained at a different instant of timerelative to the interval of scanning by the first vidicon 60.Accordingly, the output pulse from the first delay line 62 correspondingto illumination by source 56 occurs at a different time relative to thescanning interval of the first vidicon 60 than would the output pulsecorresponding to the illumination by the source 50. Thus the display onthe second storage screen 78 shows a point representing the location ofsource 56 at a location which differs from that of the image point whichrepresented the location of the source 50.

The imaging system 22 is linear and accordingly superposition applies sothat illumination of the mask 30 by both sources 50 and 56 produces animage on the first storage screen 54 which has the form of thesuperposition of the two individual images resulting from illuminationby source 50 and source 56. Similarly, the output signal of the firstvidicon 60 attained upon a scanning of the first storage screen 54 isthe superposition of two chirp waveforms. The first delay line 62responds to the superposition of the two chirped waveforms in the samemanner that it responds to each of the waveforms individually andaccordingly provides two output pulses corresponding in time to thelocations of the sources 50 and 56. Thus, there appears on the secondstorage screen 78 two image points corresponding to the locations of thesources 50 and 56. By an extension of the superposition principle itbecomes apparent that with a multiplicity of sources of high energyradiation in the object 34, such as for example, the individualradioactive molecules of the radio pharmaceutical within the thyroidgland 21, a multiplicity of image points appear on the second storagescreen 78, each of these points corresponding to the locations of theindividual sources of the high energy radiation in the object 34. Thus,there appears on the second storage screen 78 a partially unscrambledimage of the object 34, the image being unscrambled in the horizontaldirection due to the decoding by the first vidicon 60 and first delayline 62 but still being scrambled in the vertical dimension.

The second step in the decoding of the image of the mask 30 is performedby the second vidicon 82 and the second delay line 84. The secondvidicon 82 scans the image on the second storage screen 78 in thevertical direction and provides a corresponding chirp waveform which isapplied to the second delay line 84. The second delay line 84 operatesin the same manner as does the first delay line 62 and, accordingly, itresponds to the chirp waveform signal from the second vidicon 82 byproviding a set of output pulses corresponding to the locations in thevertical plane of the sources of high energy radiation of the object 34.The output pulses of the second delay line 84 are transmitted to theoutput display 28 which shows a fully unscrambled or decoded image ofthe object 34. Thus, it is seen that the first vidicon 60 and the firstdelay line 62 resolve the locations of the sources such as the sources50, 56 and 58 in the horizontal direction wile the second vidicon 82 andsecond delay line 84 resolve the locations of the sources 50, 56 and 58in the vertical direction.

Referring now to FIGS. 5 and 6 there are shown two plan views of delaylines. In the preferred embodiment of FIG. 2, the first delay line 62and the second delay line 84 are identical since the mask 30 of FIG. 3has the same condiguration and arrangement of apertures 32 in both therows and the columns. Accordingly, FIGS. 5 and 6 are equally applicableto both the first delay line 62 and the second delay line 84. The delayline 86 of FIG. 5 comprises an elongated piezoelectric crystal 88 uponwhich is mounted a pair of interdigital electrical networks, oneinterdigital network 89A serving as the input for generating surfaceacoustic waves on the crystal 88 and a seond interdigital network 898located at the output end of the crystal 88 for extracting an electricalsignal from the crystal 88. The input interdigital network 89A comprisesa pair of opposed interlaced combs 90 and 92 having fingers 94, four ofwhich are designated 94A-D, which are spaced in accordance with apredetermined format. In addition, the length of the fingers 94 may bevaried in a prescribed format as shown with the fingers 96 of delay line95 in FIG. 6. The varying degrees of overlapping between the fingers 96of the opposed combs 98 and 100 provide varying degrees of coupling ofenergy between the interdigital network 102 and the crystal 104. Thedesign of a delay line such as the delay line 86 is described in the US.Fat. to J.H. Rowen No. 3,289,114 which issued on Nov. 29, I966, and inan article entitled Tapping Microwave Acoustics for Better SignalProcessing by L. Altman, ].H. Collins and P.J. Hagon which appeared inElectronics p. 94 et seq. Nov. 10, 1969.

The input terminals to the delay line 86 comprise extensions of the pairof combs 90 and 92. An input electrical signal having a voltage V isapplied across the two terminals. The fingers 94A and 94B are spacedapart a distance X while the fingers 94C and 94D are spaced apart by adistance Y. The electrical energy in the input signal is coupled intothe crystal 88 and transformed into mechanical energy of the crystal 88at a first frequency dependent on the spacing X and at a secondfrequency dependent on the spacing Y. The mechanical energy is indicatedat a wave 106 shown by a series of wavey arrows. Thus, energy is coupledat the first frequency between fingers 94A, 94B and the crystal 88, andat the second frequency between the fingers 94C, 94D and the crystal 88.

The reverse mechanism mainly the conversion of the mechanical energy ofthe crystal 88 into electrical energy occurs at the output end of thedelay line 86. In the output interdigital network 89B there are also apair of fingers spaced at a distance X, namely, fingers 108A and 1088,and similarly there are also a pair of fingers spaced at a distance Y,namely, fingers 108C and 108D. Mechanical energy at the first frequencyis coupled out from the crystal 88 by means of fingers 108A and 1083,and that at the second frequency by means of the fingers 108C and 108D.The delay line 86 is made dispersive to provide different delays atdifferent frequencies by arranging the input and output interdigitalnetworks 89A and 893 such that they are the mirror images of each otherwith respect to the centerline of the crystal. Thus, for example, thetwo spacings of distance X are symmetrically located relative to thecenterline of the crystal 88 and similarly the two spacings of distanceY are symmetrically located relative to the centerline of the crystal88, however the spacings of distance X are further away from thecenterline than the spacings of distance Y. As a result, energy at thefirst frequency traverses a greater portion of the crystal 88 than doesenergy of the second frequency, and consequently experiences a greaterdelay. Thus where the signal voltage V, is a chirped signal in which theinstantaneous frequency is increasing, the energy at which of thesefrequencies is selectively delayed with the result that substantiallyall of the energy appears at the output terminals at the same instant oftime. Thus, the output voltage V is a pulse of energy approximating animpulse.

The delay line 86 is commonly referred to as a surface wave delay linesince accoustic energy in the form of mechanical vibrations travel alongthe surface of the crystal as indicated by the wave 106. The delay line86 can be designed to approximate various filter characteristics byadjusting the amount of overlap between adjacent fingers of opposedcombs as shown by fingers 96 of in FIG. 6. For example, if it is desiredto pass energy at one frequency but attentuate energy at a secondfrequency than a relatively large amount of overlap is provided for thefirst frequency and a minimal amount of overlap is provided at thesecond frequency. In this way a relatively large amount of energy iscoupled at the first frequency and passes through the delay line 86while a minimal amount of energy is coupled at the second frequencyresulting in attenuation at that frequency.

Returning again to FIG. 2 a scan controller 110 coordinates thescannings of the first and second vidicons 60 and 82, the second storagetube display and the output display 28 so that each of these scanningsoccur with the correct temporal relationship. Accordingly, in theoperation of the second storage tube display 80 the successive horizondeflections of the cathode-ray-tube beam are delayed from thecorresponding horizontal line scans of the first vidicon 60 by an amountof time equal to the minimum time delay of the first delay line 62, thatis, the amount of time required for energy to first appear at the outputof the first delay line 62 in response to a signal from the firstvidicon 60. the scanning of the second vidicon 82 is delayed until thefull image has been composed upon the second storage screen 78. Theoperations of the output display 28 and of the second vidicon 82 aredelayed by an amount equal to the minimum delay time of the second delayline 84. The aforesaid temporal relationships among the variousscannings assure that the images provided on the various displays areappropriately centered relative to the display. It is also apparentthat, alternatively, the horizontal and vertical scanning procedures maybe interchanged such that the image on the first storage screen 54 isvertically scanned while the image on the second storage screen 78 ishorizontally scanned.

By way of alternative embodiments it is noted that the first storagetube display 52 and the first vidicon 60 could be replaced by a singlewell-known scan converter tube (not shown) comprising read and writeelectron beams and a storage screen if the persistence of the storagescreen is sufficient to permit the development of the image of the mask30 during the successive impacts of quanta of radiant energy upon thescintillator 36. The use of scan converter tubes is well known and isnot shown in the figures. Similarly, the second storage tube display 78and the second vidicon 82 may be replaced with a single scan convertertube.

Focusing of the imaging system 22 of FIG. 2 to provide the desiredspacings between the object 34, the mask 30 and the detector assembly 24is accomplished as follows. The object 34, mask 30 and detector assembly24 are spaced apart such that the shadow or image of the mask 30 due toillumination by a single source of the high energy radiation is smallerthan the scintillator 36. Thereby, each of the shadows of mask 30corresponding to illumination by successive sources, such as sources 50,56 and 58, fall wholly within the area of the scintillator 36. If thesize of the mask 30 approximates that of the scintillator 36 than it isapparent that the shadow due to illumination by source 58 may lie whollywithin the area of the scintillator 36 while the shadow due toillumination by source 50 has its upper edge outside the area of thescintillator while the shadow due to illumination by source 56 has itslower edge outside the area of the scintillator. As a result with anoverly large mask not all of the sources such as the sources 50 and 56receive the full benefit of the mask' 30 during the formation of theimages of these sources by the imaging system 22. On the other hand, alarge mask permits increased resolution in that a greater range ofaperture sizes may be formed within the mask.

The spatial bandwidth, and hence, the resolution attainable with theimaging system 22 is determined by the difference between the smallestaperture size and the largest aperture size of the mask 30. A largenumber of apertures 32 are utilized to insure small gradations in sizebetween adjacent apertures, therby providing a smooth transition in thespatial frequency domain from the lowest spacial frequency to thehighest spatial frequency and, thereby further providing output signalsfrom the first and the second vidicons 60 and 82 which have a smoothspectral distribution. As a result, the delay lines 62 and 84, havingtemporal impulse response functions which are the inverse of the vidiconoutput signals, function as pulse compression filters providing minimalside lobes. If the spatial bandwidth is retained but the number ofapertures 32 in the mask 30 is decreased, that is there are larger jumpsin size between adjacent apertures 32, then the extent of the side lobesin the output signals from the delay lines 62 and 84 increases.Therefore, it is seen that it is desirable to use a large mask yetretain a sufficiently small size such that all the sources of the highenergy radiation provide shadows which fall within the area of thescintillator 36. It is convenient to regard the field of view of theimaging system 22 as being the maximum spacings between sources of thehigh energy radiation such that there is no reduction in the attainableresolution due to an extension of a shadow of the mask 30 beyond thearea of the scintillator 36.

Another advantage of a large mask is the increased aperture of theimaging system 22 due to the fact that more rays of radiant energy areintercepted by the mask 30 and processed. A larger aperture meansdecreased viewing time so that, in the case of the patient of FIG. 1being treated for a thyroid ailment, less exposure time is required toobtain the radiograph of the thyroid gland 21. In particular, it isnoted that the mask provides a greater aperture or efficiency than doeseither the pin hole version of the Anger camera or the collimatorversion of the Anger camera, both disclosed in the aforementioned patentto Anger. As compared to the pinhole camera, the imaging system 22attains a greater efficiency because there is a larger total aperturedue to the summation of all the apertures 32 in the mask 30; and withreference to the collimator version of the Anger camera, the imagingsystem 22 attains a greater efficiency due to the fact that a relativelylarge number of high energy photons strike the septal separations withinthe collimator so that only those photons directed in a directionparallel to the collimator axis reach the scintillator.

For precise focusing of the imaging system 22 on the object 34, apredetermined scan rate provided by rate selector 112 is applied bymeans of the scan controller 110 to the first vidicon 60, the scan ratebeing selected so that the image of a point source on the first storagescreen 54 is scanned in a time interval ofa preset value independentlyof the size of this image. It is readily apparent that the dimensions ofthis image are proportional to the dimensions of the mask 30 and,furthermore, related to the distance from the object 34 to the mask 30and from the mask 30 to the scintillator 36. For example, with referenceto the patient 20 of FIG. 1, if the patient were to move away from theimaging system 22, then the image formed upon the first storage screen54 would become smaller. If the scan rate applied by the scan selector112 were to remain at a preset value, then it is apparent that theimage, due to its reduced size, would be scanned in a correspondinglyreduced interval of time with the result that the frequency componentsoccurring in the output signal of the first vidicon would be scaled to acorrespondingly higher value which may be greater than that for whichthe first delay line 62 has been designed. To compensate for this motionof the patient 20 of FIG. I, either the mask 30 is to be repositionedfurther away from the detector assembly 24 by suitable means (not shown)thereby restoring the image on the first storage screen 54 to itsoriginal size, or alternatively, by reducing the scan rate applied bythe scan selector 112 so that the reduced size image is scanned in atime interval having the preset value. Since the field of view of theimaging system 22 is dependent on the relative distances from the object34 to the mask 30 and from the mask 30 to the scintillator 36, it ispreferable to adjust the focusing by means of the scan rate applied bythe scan controller 110 to the first vidicon 60.

The following relationships, indicated mathematically, are useful in thedesign of the imaging system 22. The compression ratio resulting fromthe use of the chirped signal from the first vidicon 60 and theconjugate time delay characterlstic of the first delay line 62 may beexpressed as the ratio of the width of an image on the first storagescreen 54, corresponding to a point source of radiation, to the width ofthe mask 30. The compression ratio C is given by where 1,, is the widthof the mask 30 and BW, is the spatial frequency bandwidth which is givenas the difference between the minimum and the maximum spatialfrequencies of the mask pattern. For example, a uniform arrangement ofl0 equal apertures within a distance of 1 inch would give a spatialfrequency spectrum described by a single line of value 10 line-pairs perinch. As a further example consider a mask having a chirped pattern inwhich the apertures are spaced at a rate of 200 apertures per inch nearone edge of the mask and at a rate of apertures per inch near theopposite edge of the mask. In this example, the spatial frequencybandwidth is 100 line-pairs per inch.

The field of view mentioned hereinabove is given in the followingequation:

where Fy is the field of view, s is the distance between the object andthe mask, s is the distance between the mask and the image plane at theface of the scintillator 36, and 1, is the length of the image plane atthe scintillator 36.

The resolution in line-pairs per inch is given by where R, is theresolution in the horizontal dimension of the image on the first storagescreen 54 in line-pairs per inch, BW is the fractional bandwidth of thefirst delay line 62 which is the bandwidth of the delay line divided bythe maximum frequency of the delay line, and R, is the minimumresolution of the scintillator 36 which depends on such factors as thethickness of the scintillator 36.

By way of example in constructing the preferred embodiment of theimaging system 22, the first and the second delay lines 62 and 84 areeach operated over a frequency of from 2.8 megahertz to 4 megahertz, andare fabricated from a quartz crystal 8% inches in length; each of theinterdigital networks 89A and 89B comprise a pair of opposed combs, eachcomb having approximately 100 fingers. The mask 30 in the case of X-radiation is a thin lead film of approximately 3 microns (3X10' meters)in depth. The transparent substrate 65 (seen in FIG. 3) for supportingthe thin film is fabricated from a /8 inch thick plate of aluminum. Forgamma radiation at a energy of 100 Kev the thickness of the lead film isapproximately 1% millimeter. The mask 30 has a square shape, each sidebeing 2 inches long. There are 100 apertures along a side giving a totalnumber of apertures of 10,000.

The number of apertures that can be placed upon a 2 inch square mask islimited by the thickness of the mask, since it is desired to provide anaperture size which is much greater than the depth of the mask to avoidproducing a structure similar to the collimator shown in theaforementioned patent to Anger. As shown in FIG. 2 the rays of radiationindicated by the lines 38A-D fan out from the source 50 through theapertures in the mask 30 to illuminate the scintillator 36; suchillumination of the scintillator 36, namely, by diverging rays, would beprecluded by the collimator structure shown in the aforementioned patentto Anger.

The size of the mask 30 is smaller than the size of the scintillator 36for reasons which can be readily appreciated by the following example.If the scintillator 36 were to have a width of 4 inches and the maskwere to have a width of 2 inches, then for an equal spacing of the maskbetween the object 34 and the scintillator 36 a point source on theobject 34 could completely illuminate the scintillator 36 with an imageor shadow of the mask 30. Then, if a second source were positionedalongside the first source to illuminate the scintillator 36, the shadowcast by the mask 30 due to the second source would not fall wholly uponthe scintillator 36. In view of the equations given above for the fieldof view and the resolution, it is apparent that the imaging is morereadily accomplished if the mask size is less than half the size of thescintillator 36. For example, a 2 inch mask and an 8 inch or inchscintillator may be utilized.

Referring now to FIG. 7 there is shown an alternative embodiment of theimaging system which may be utilized for providing a radiograph of theobject 34. The radiation from object 34 passes through the apertures inthe mask 30 to impinge upon a photographic film 122 carried by a reelassembly 124. An aperture stop 126 delineates the boundaries of theimage formed upon the film 122. In this embodiment the radiograph is anegative rather than the positive provided in FIG. 2. The film 122 isdeveloped by any suitable means (not shown) so that the image on thefilm can be illuminated by a light beam. A beam of light l28 is providedby Ian tern 130 and collimated by lens 132 to illuminate the image onthe film 122 which has been formed in response to radiation passingthrough the mask 30. In this embodiment the film serves as both thedetector assembly 24 and the first storage tube display 52 of theembodiment of FIG. 2. The remaining portions of the embodiment of FIG.7, such as the vidicon 134, which corresponds to the first vidicon ofFIG. 2 are the same as those shown in FIG. 2.

Referring now to FIGS. 8 and 9 there is shown an alternative embodimentof the invention wherein the spatial modulation of the high energyradiation which was provided by the mask 30 of FIG. 2 is now provided bya source of radiation 136 which comprises a novel arrangement ofemissive material such as radioactive ma terial 138 deposited on asubstrate 140 and selectively etched to provide areas of radiationhaving the same shape and configuration as the apertrues 32 of the mask30 of FIGS. 2 and 3. The object 142 is partially opaque so that pointsof the object 142 such as the points 144, 146 and 148 are illuminated bythe source of radiation 136 to form an image upon the detector assembly24. The detector assembly 24, processor 26 and output display 28 shownin FIG. 8 are the same as those utilized in FIG. 2. In FIG. 2 each pointsource, such as the source 50, is transformed to a shadow of the mask 30at the detector assembly 24. Analogously, in FIG. 8 each point of theobject 142 is transformed into an image at the detector assembly 24, theimage depending on the form of the pattern of radioactive material 138deposited upon the substrate 140 of the source 136.

Referring now to FIG. 10 there is an X-ray radiographic system 150utilizing a source 152 of X-rays to be described hereinafter, aphotographic film 154 carried by a reel assembly 156, and an object 158to be illuminated by the source 152 for forming an image on the film154. After forming the image on the film 154 the film is developed byany suitable means (not shown) and positioned such that the image fallswithin a beam of light 160 formed by a lantern 162 and collimating lens164 for processing by the optical system 166. The optical system 166 isof a well known form and is often used for extracting information from aradiograph. The optical system 166 comprises a pair of lenses 168 and170 with a spatial optical filter 172 placed between the lenses, and ascreen 174 upon which a filtered manifestation of the image appears. Asis well known spatial filtering is used in a manner analogously to thefiltering of time domain signals to extract those portions of the signalhaving a desired frequency characteristic and suppressing other portionsof the signal having other frequency characteristics. The spatial filter172 has portions of varying opacity to inhibit the passage of selectedspacial frequencies. In this way certain features of a radiograph aremade more readily visible.

Of particular interest is the fact that a broad band optical signal canproduce greater definition in a radiograph when proper filtering isemployed. A point source of high energy radiation provides a relativelylarge spatial bandwidth. On the other hand a relatively large sourceprovides a relatively narrow spatial bandwidth. As is well known, thesources of radiation which most closely approximate the point source andtherefore have the largest spatial bandwidth provide a radiograph withthe best definition or, equivalently, the clearest picture. The use ofthe novel source 136 (of FIG. 9) of this invention as the source 152 inthe radiographic system 150 of FIG. 10 provides radiation having a largespatial bandwidth, the extent of the bandwidth being directly related tothe number of radiant regions (such as the regions of radioactivematerial 138) per unit area and their configuration. In particular, thesource as shown in FIG. 9 provides a chirp wave form bandwidthcharacteristic analagous to that obtained by use of the mask 30 in theimaging system 22 of FIG. 2. This broad bandwidth may be utilized inconventional spatial filtering techniques such as that shown in FIG. 10for enhancing the definition of an object, or alternatively may beutilized in the system of FIG. 8 as described hereinbefore.

Referring now to FIG. 11, there is shown an alternative embodiment ofthe imaging system of the invention wherein the scanning of thescrambled image on the face of the detector assembly 24 is accomplishedin a two-step procedure in which the horizontal scanning is donemechanically and the vertical scanning is done electronically. In thisembodiment the mask 30 of FIG. 2 is replaced with a mask 176 having asingle column of apertures 178 which provides a scrambled image having aheight similar to the height obtained with the embodiment of FIG. 2, buthaving a width which is sufficiently narrow so that the scrambled imageapproximates a line image. A collimator 180 comprising a single slot 182out within a lead block 184 is used to collimate the rays of radiationemanating from the object 34 so that only those rays within the columnof apertures 178 can pass to the detector assembly 24.The mask 176 ismounted upon a substrate 186 similar to the rigid substrate 65 of FIG.3. The collimator 180, the mask 176, and a mask substrate 186 aresupported upon a movable rack 188 which is slidably mounted upon a track190 affixed to a block 191 and tightened in position against the'track190 by means of set screw 192. The movable rack 188 is utilized toposition the mask 176 and the collimator 180 for focusing the image ofthe object 34 in a manner similar to that described with reference tothe embodiment of FIG. 2.

In the embodiment of FIG. 11 the detector assembly 24 and a storage tubedisplay 194 function in the same manner as the detector assembly 24 andthe first storage tube display 52 of FIG. 2. A vidicon 196 is programmedby a scan controller 198 to scan a single vertical line scanrepetitively, rather than the sequence of horizontally displacedvertical line scans that is associated with a television raster type ofscan. The output signal of the vidicon 196 is processed by a delay line200 and subsequently displayed on an output display 202 in a mannersimilar to that described in FIG. 2 with reference to the second delayline 84 and the output display 28. Each point of the scrambled image ofthe line scan displayed on the storage screen 204 corresponding to apoint, such as point 206, on the object 34 is compressed by the delayline 200 into a single point of the line displayed on the output display202.

The mechanical scanning in the horizontal direction is accomplished bymeans of a mechanical scanner 208 comprising a rod 210, slidably mountedthrough the block 191 and a threaded rod 212, passing through a tappedhole in the block 191, which support the movable rack 188. The rod 210and the threaded rod 212 are supported at their first ends by a mount214 and at their opposite ends by a second mount, similar to mount 214but not shown in the Figure. The threaded rod 212 is journalled in themount 214 and passes through the mount 214 to make contact with a gear216 by which the threaded rod 212 is rotated in the manner of a wormdrive to impart a horizontal displacement in the position of the block191 in accordance with the amount of rotation of the threaded rod 212and the gear 216. The gear 216 is driven by a motor 218 through a pinion220 mounted on the shaft (not shown) of the motor 218 and meshing withthe gear 216. The motor 218 is a well known form of electric motor, suchas a shunt wound motor, wherein the direction of rotation of the motorshaft can be varied electrically, as for example, by reversing thedirection of current which energizes the rotor winding while retainingthe direction of current which energizes the stator winding. In this waythe movable rack 188 can be moved back and forth in the horizontaldirection.

An electrical signal representing the position of the block 191 isprovided by a potentiometer 222 mechanically connected to gear 216 via agear train 224, indicated diagrammatically in FIG. 11, having a pinion226 which meshes with the gear 216. In this way rotation of thepotentiometer shaft (not shon) is proportional to the rotation of thethreaded rod 212 and, therefore, to the displacement of the block 191.

The horizontal and vertical scanning are coordinated by means of thescan controller 198 which provides a signal along line 230 to thestorage tube display 194 for erasing the line image on the storagescreen 204 after each vertical scan of the vidicon 196 so that a newscrambled image in the form of a vertical line on the storage screen204' can be composed for each position of the block 191. The outputdisplay 202 has a storage screen to permit direct viewing of theinformation provided by the successive line scans. The mechanicalscanner 208 is driven in response to signals along line 232 provided bythe scan controller 198. Signals from the potentiometer 222 representingthe position of the block 191 are transmitted to the scan controller 198along line 234. Each line scan by the vidicon 196 is provided inresponse to a signal on line 236 from the scan controller 198. Thescanning rate is selected by means of a rate selector 238 which connectswith the scan controller 198 and functions in a manner similar to thatshown in FIG. 2 with reference to the rate selector 112 for focusing theimaging system.

The output display 202 employs a well known cathode ray tube (not shown)for displaying an image of the object 34. Deflection signals for thecathod ray tube of the output display 202 are provided in accordancewith signals from the scan controller 198 along line 240. The verticaldeflection signals for the output display 202 correspond to the verticaldeflection signals of the vidicon 196, and the horizontal deflectionsignals for the output display 202 correspond to the signals along line234 from the potentiometer 222.

It should be noted that the image displayed on the output display 202 ofFIG. 11 differs from that displayed by the output display 28 of FIG. 2in that the output display 28 provides compression in two dimensionswhile the output display 202 of FIG. 11 provides an image which iscompressed in only the vertical direction. Compression in the verticaldirection, only, has occured by virtue of the fact that the mask 176 ofFIG. 11 provides only a single column of apertures 178, while theimaging system 22 of FIG. 2 the mask 30 has a two-dimensional array ofboth columns and rows of apertures 32.

Referring now to FIG. 12 there is shown an alternative embodiment of theimaging system of FIG. 2 wherein the detector assembly 24 and the firststorage tube display 52 are replaced by an image intensifier 242comprising a scintillator 244, a glass plate 246 contiguous to thescintillator 244 and supporting a photocathode 248 in the form of a thinfilm, and an anode 250 which are enclosed by an envelope 252 formaintaining a vacuum between the photocathode 248 and the anode 250. Adifference of potential is maintained between the photocathode 248 andthe anode 250 by a suitable voltage source (not shown). Electronsemitted by the photocathode 248 are focused by suitable means, such as awell known magnetic deflection system (not shown) concentric to theenvelope 252 for providing an image on a screen 254.

The object 34 and mask 30 are positioned in front of the imageintensifier 242. In response to radiation emitted by object 34 andpassing through apertures 32 in mask 30 to the scintillator 244, thescintillator 244 emits optical photons which interact with thephotocathode 248 causing it to emit electrons. The sites on thephotocathode 248 from which the electrons emanate correspond to thesites on the scintillator 244 at which high energy photons from object34 impact. Accordingly, the image on the screen 254 has the same form asthe image appearing on the first storage screen 54 of FIG. 2. The screen254 is then scanned by vidicon 256 in the same manner as the storagescreen 54 of FIG. 2 is scanned by the first vidicon 60. The remainder ofthis alternative embodiment of the imaging system is the same as that ofthe imaging system 22 of FIG. 2 and is therefore not shown in FIG. 12.

It is understood that the above described embodiments of the inventionare illustrative only and that modifications thereof will occur to thoseskilled in the art. Accordingly, it is desired that this invention isnot to be limited to the embodiments disclosed herein, but is to belimited only as defined by the appended claims.

What is claimed is: 1. In combination: means for spatially distributingsequentially occurring quanta of radiant energy in a coded format, saiddistribution having a succession of first regions and a succession ofsecond regions, the transmissivity of said second regions to saidradiant energy being less than the transmissivity of said first regionsto said radiant energy, said first regions being interspersed among saidsecond regions and being arranged in accordance with said format; meansresponsive to said quanta of radiant energy for providing signals havinginformation relative to the locations of said quanta of radiant energy,said signal providing means including means for converting radiantenergy into energy carried by electronic charges;

said signal providing means being spaced apart from said distributingmeans such that quanta of radiant energy emanating from loci which arespaced apart and equidistant from siad said distributing means canimpinge upon a single point of said signal providing means; and

means having information relative to said format for decoding saidsignals to extract therefrom information relative to locations of pointsof emanation of said quanta of radiant energy.

2. The device as defined by claim 1 wherein said decoding means providesan image and comprises:

means for scanning the information of said signals,

said scanning means providing a time modulated signal in response to thelocations of said quanta; and

means for filtering said time modulated signal to provide a point ofsaid image.

3. The device as defined by claim 2 further comprising:

means responsive to said filtering means for displaying said point ofsaid image; and

means for coordinating said display means with said scanning forpositioning said point within said image.

4. In combination:

means responsive to quanta of radiant energy emitted sequentially from asource of such radiant energy, said means inhibiting the passage of suchones of said quanta being emitted in any one of a plurality ofpredetermined directions, said means permitting the passage of at leastsome of said quanta of radiant energy emitted from said source in otherpredetermined directions, said means being further structured forproviding a sequence of regions of inhibited passage and a sequence ofregions of permitted passage of quanta of radiant energy, said regionsof inhibited passage and permitted passage varying in size in accordancewith a predetermined spatial code;

means including scintillation means for detecting the presence of suchones of said quanta of radiant energy which have passed through saidimpeding means, said detecting means providing signals havinginformation relative to the locations of such quanta;

said detecting means and said inhibiting means being positioned relativeto each other and relative to said source such that quanta of radiantenergy emitted from separate points of said source and passing throughseparate ones of said regions of permitted passage can impinge upon asingle point of said detecting means; and

means responsive to said signals of said detector means for decodingsaid information to provide an image of said source of radiation.

5. In combination:

means for illuminating an object with quanta of radiant energy, saidmeans having regions of emission of said radiant energy interspersedamong regions of non-emission, said regions of emission being arrangedin a spatially coded pattern, said means being positioned relative tosaid object to permit quanta of radiant energy from different ones ofsaid emissive regions to impinge upon a single point of said object;

means responsive to the transmissivity of said object to said radiantenergy for detecting radiant energy transmitted through said object,said detecting means providing information relative to the locations ofsuch ones of said quanta of radiant energy arriving at said detectingmeans within a predetermined interval of time; and

means responsive to said information of said detecting means fordecoding said spatially coded pattern to provide an image of saidobject.

6. In combination:

means responsive to rays of radiation emitted from an object havingsources of such radiation for modulating said radiation while retainingthe directions .of said rays, said means comprising an array ofradiation transmissive regions interspersed among relatively opaqueregions, said transmissive regions being arranged in accordance with apredetermined format;

means for detecting said modulated radiation, said detecting means beingpositioned relative to said modulating means such that one of said raysof radiation transmitted via one of said transmissive regions and asecond of said rays of radiation transmitted via a second of saidtransmission regions can impinge upon a single point of said detectingmeans, said detecting means providing a signal having informationrelative to said format and to the locations of such ones of said raysof radiation which pass through said transmissive regions; and

means for correlating said first signal with the arrangement of saidtransmissive regions in said predetermined format to provide an image ofsaid object, said correlating means including means for scanning saiddetector signal and means for filtering the output of said scanningmeans, said filtering means being frequency dispersive.

7. The device defined by claim 6 wherein said correlating means furthercomprises:

means for generating a second signal which is modulated with saidinformation relative to said format and further modulated with saidinformation relative to said rays of radiation; and

second means for providing a filtering function and filtering saiddetector signal, said second filtering means having a temporal weightingfunction complementary to the arrangement of said transmissive regionsin said format for providing an image of said object.

8. In combination:

means responsive to the energy of particles moving along substantiallylinear paths for modulating the intensity of said particles, saidmodulating means comprising an array of barrier elements havingpredetermined sizes and being arranged in a predetermined format;

means for detecting selected ones of said particles which pass betweensaid barrier elements to provide a signal having information relating tothe locations of said selected particles, said detecting means beingspaced from said modulating means to permit particles moving along apair of said paths disposed on opposite sides of a barrier element toimpinge on a single point of said detector means; and

means for comparing said signal with said format to extract saidinformation for forming an image.

9. An imaging system responsive to radiation emitted from an object,said imaging system comprising:

means for spatially modulating said radiation while retaining thedirection of rays of said radiation, said moduating means comprising anarray of radiation transmissive regions having differing sizes andarranged in a predetermined configuration;

means responsive to said spatially modulated radiation for forming afirst image having information relative to said object and relative tosaid predetermined configuration, said first image forming means beingpositioned relative to said modulating means such that one of said rayspassing through one of said transmissive regions and a second of saidrays passing through a second of said transmissive regions can impingeupon a single point of said first imaging forming means;

a delay medium; and

means for transmitting portions of said first image through said delaymedium, said delay medium imparting to each of said portions adifferential delay complementary to a corresponding portion of saidpredetermined configuration for providing said information relative tosaid object.

10. The system as defined by claim 9 further comprising means responsiveto said transmission means for displaying an image of said object.

11. The system as defined by claim 10 wherein said transmission meanscomprises:

means for scanning said first image to provide a time modulated signalcontaining information relative to said predetermined configuration; andwherein said delay medium comprises means for generating surface waves.

12. The system as defined by claim 11 wherein said modulating meansfurther comprises means for impeding radiation having an energy lowerthan a preset magnitude.

13. An imaging system comprising:

a source emitting radiation for illuminating an object, said sourcebeing adapted to provide said radiation with a spatially modulatedpattern, said source having a series of spaced apart luminous regionseach of which is positioned for illuminating a common point on saidobject;

means responsive to said spatially modulated radiation for forming afirst image having information relative to said object and relative tosaid pattern;

a delay medium; and

means for transmitting portions of said first image through said delaymedium, said delay medium imparting to each of said portions adifferential delay inverse to a corresponding portion of said patternfor providng said information relative to said object.

14. The system as defined by claim 13 further comprising meansresponsive to said transmission means for displaying an image of saidobject.

15. The system as defined by claim 14 wherein said transmission meanscomprises:

means for scanning said first image to provide a time modulated signalcontaining information relative to said pattern; and wherein said delaymedium comprises means for generating surface waves.

16. An array of regions each of which comprises a radiation emissivematerial and has a predetermined size, each of said regions being spacedapart such that each of said sizes and each of said spacings havepreselected magnitudes for providing a predeterminedspatial frequencycharacteristic, and means for positioning each of said regions in saidarray, a plurality of regions of said array of regions being arranged ina sequence according to the magnitudes of their sizes and their spacingsordered by monotonically increasing magnitudes to provide said spacialfrequency characteristic with a characteristic of a chirp wave form.

17. In combination:

means responsive to rays of radiation emitted from an object havingsources of such radiation for modulating said radiation with a spatialpattern while retaining the directions of said rays, said meanscomprising an array of radiation transmissive regions illuminated bysaid radiation and interspersed among relatively opaque regions, saidtransmissive regions being configured and arranged in accordance with apredetermined format such that said spatial pattern contains informationrelative to said format; and

means responsive to the locations of said modulated rays of radiationfor correlating said modulated rays with said format to derive an imageof said object, said correlating means being positioned relative to saidmodulating means such that one of said rays passing through one of saidtransmissive regions and a second of said rays passing through a secondof said transmissive regions can impinge upon a single point of saidcorrelating means.

18. The device as defined by claim 17 wherein said correlating meanscomprises means for varying said responsivity in accordance with thespacing between said object and said modulating means whereby saiddevice is focused.

19. In combination:

means responsive to rays of radiation emitted from a source of radiationfor modulating said radiation, said means comprising an array ofradiation transmissive regions interpersed among relatively opaqueregions, said transmissive regions being arranged in accordance with apredetermined format;

means including scintillation means for detecting said modulatedradiation for providing a signal having information relative to saidformat and to the locations of such ones of said rays of radiation whichpass through said transmissive regions;

said detecting means being spaced apart from said modulating means topermit rays of radiation passing through noncontiguous ones of saidtransmissive regions to impinge upon a common point of said detectingmeans; and

means for correlating said signal with said predetermined format toprovide the direction of said source.

20. In combination:

means responsive to the energy of particles emanating from a source ofsuch particles and moving along substantially linear paths formodulating the energy of said particles, said modulating meanscomprising an array of barrier elements having predetermined sizes andbeing arranged in a predetermined format;

means for detecting selected ones of said particles which pass betweensaid barrier elements to provide a signal having information relating tothe locations of said selected particles, said barrier elements beingspaced from said detecting means to permit particles traveling onopposite sides of one of said barrier elements to impinge upon a commonpoint of said detecting means; and

means for comparing said signal with said format to extract saidinformation to provide the direction of said source.

21. In combination:

means for modulating the spatial distribution of quanta of radiantenergy illuminating an object,

said spatial modulation having a predetermined format;

means responsive to the locations of quanta of radiant energy forreceiving said quanta of radiant en ergy, said receiving meanspreserving information relative to said locations; and

means for filtering said received radiant energy concurrently with thereception of quanta of radiant energy by said receiving means, theimpulse response function of said filtering means having a formatcomplementary to said spatial modulation format for providinginformation relative to said object.

22. A scanning system comprising:

means for modulating the distribution of radiant energy emanating froman object, said modulating means having a succession of radiationtransmissive regions of differing sizes, said radiation transmissiveregions being arranged in a sequence of monotonically increasing sizesin a first direction and in a second direction;

means for detecting said quanta of radiant energy,

said detecting means providing an electrical impulse in response to thereception of a quanta of said radiant energy, said detecting means beingspaced apart from said modulating means to permit radiant energy passingthrough different ones of said transmissive regions to impinge upon acommon point of said detecting means;

means for storing said impulses, said storage means preserving datarelative to the locations of the received quanta of radiant energy;

means for filtering the data in said storage means,

said filtering means having a phase characteristic which is the inverseof the spatial modulation format of one of said sequences oftransmissive regions;

second storage means for receiving data from the filtering means;

second filtering means for filtering the data in said second storagemeans, said second filtering means having a phase charactertistic whichis inverse to that sequence of said transmissive regions in a seconddirection; and

means responsive to the data filter by said first filtering means andthe data filtered by said second filtering means for providing imagepoints of said object in a first direction and in a second direction.

23. The scanning system of claim 22 wherein said first filtering meansincludes means for scanning said first storage means in accordance witha predetermined format.

24. The scanning system in accordance with claim 23 wherein saidfiltering means comprises a surface wave delay line.

25. The scanning system in accordance with claim 24 wherein said firststorage means comprises a storage tube display.

26. The scanning system in accordance with claim 25 wherein saidscanning of said first storage means provides a chirped frequency signalto said first filtering means.

27. A scanning system comprising:

means for placing a source of radiant energy in an object to be scanned;

means for detecting said radiant energy;

means interposed between said object and said detecting means forcasting a shadow of said radiant energy upon said detecting means, saidshadow comprising a plurality of shaded regions varying in size andposition in accordance with a predetermined format;

said shadow casting means being spaced from said detecting means suchthat a second source of radiant energy located alongside the aforesaidsource of radiant energy casts a second shadow comprising a plurality ofshaded regions which overlap the shaded regions of the aforesaid shadow;

means coupled to said detecting means for storing data relative to theconfiguration of said shadow; and

means for processing said stored data while said radiant energy isincident upon said detecting means, said processing means providing datarelative to the form of said object.

28. In combination:

an array of sources of radiant energy positioned to illuminate anobject, said sources having differing sizes and being arranged in apredetermined format;

means for detecting quanta of said radiant energy, said detecting meansbeing positioned relative to said object such that radiant energy from aplurality of said sources can impinge upon a common point of said objectand in passing by said object is incident upon said detecting means,said detecting means providing data relative to the spatial positions ofsuch ones of said quanta of radiant energy which are incident upon saiddetecting means; and

means for filtering the data provided by said detecting means, saidfiltering means having a phase characteristic functionally dependentupon said format to provide data relative to the form of said object.

29. In combination:

means for altering the spatial distribution of gamma rays, said gammarays being utilized for illuminating an object, said altering meanscomprising a succession of radiation transmissive regions dispersedamong regions of relative opacity to gamma rays, said transmissiveregions being arranged in a predetermined format, said transmissiveregions having a depth smaller than the width of such regions;

means for detecting such ones of said gamma rays that pass through saidaltering means, said detecting means providing data relative to thelocations of said gamma rays; and

means for correlating said data with said format to provide informationabout said object.

30. A nuclear imaging system comprising:

means for altering the spatial distribution of radiation utilized forilluminating an object, said altering means comprising a succession ofradiation transmissive regions interspersed among regions of relativeopacity to said radiation, said transmissive regions being arranged in apredetermined format in the form of a chirp pattern in at least onedimension such that the transmissive regions are arranged according tosize in a monotonically decreasing array;

means for detecting rays of said radiation that pass through saidaltering'means, said detecting means including means for providing datarelative to the locations upon said detecting means where individualrays of said radiation impinge; and

means for correlating said data with said format to provide informationabout said object.

31. The nuclear imaging system in accordance with claim 30 wherein theformat of said altering means includes a chirp pattern in a seconddimension providing an array of radiation transmissive regions arrangedaccording to size in a monotonically decreasing array.

32. The nuclear imaging system in accordance with claim 31 wherein:

the detecting means further comprises means for storing said data, saiddata being stored in the form of an array of points each of whichrepresents the location of a point of impingement of a ray of radiationupon the detecting means; and wherein said correlating means comprisesmeans for scanning the array of data points of said detecting means toprovide a scan signal, said correlating means further comprising meansfor filtering said scan signal, the frequency bandwidth of said scansignal being related to the spacing between locations of said points ofimpingement of rays of radiation upon said detecting means, saidfiltering means enabling a focussing of said nuclear imaging system whenthe bandwidth of said scan signal approximates the bandwidth of saidfiltering means.

33. The imaging system in accordance with claim 32 further comprisingmeans for varying said focus.

34. The imaging system according to claim 33 wherein said variable focusmeans comprises means for varying the scanning rate of said scanningmeans of said correlating means.

35. A nuclear imaging system comprising:

means for illuminating an object with radiation, said illuminating meanscomprising a successionof radiation emissive regions interspersed amongregions of non-emission, said emissive regions being arranged in apredetermined format in the form of a chirp pattern in at least onedimension such that the emissive regions are arranged according to sizein a monotonically decreasing array;

means for detecting rays of said radiation that pass from saidilluminating means, said detecting means including means for providingdata relative to the locations upon said detecting means whereindividual rays of said radiation impinge; and

means for correlating said data with said format to provide informationabout said object.

36. The nuclear imaging system in accordance with claim 35 wherein theformat of said illuminating means includes a chirp pattern in a seconddimension providing an array of radiation emissive regions arrangedaccording to size in a monotonically decreasing array.

37. The nuclear imaging system in accordance with claim 36 wherein:

the detecting means further comprises means for storing said data, saiddata being stored in the form of an array of points, each of whichrepresents the location of a point of impingement of a ray of saidradiation upon the detecting means; and wherein said correlating meanscomprises means for scanning the array of data points of said detectingmeans to provide a scan signal, said correlating means furthercomprising means for filtering said scan signal, the frequency bandwidthof said scan signal being related to the spacing between locations ofsaid points of impingement of rays of said radiation upon said detectingmeans, said filtering means enabling a focussing of said nuclear imagingsystem when the bandwidth of said scan signal approximates the bandwidthof said filtering means; and wherein said nuclear imaging system furthercomprises means for varying said focus, said variable focus meanscomprising means for varying the scanning rate of said scanning means ofsaid correlating means.

38. In combination:

means for spatially distributing quanta of radiant energy in a codedformat, said distribution having a succession of regions of differingdimensions, said regions having differing amounts of said quanta; and

means responsive to said quanta of radiant energy for providing signalshaving data relative to the locations of said quanta of radiant energy,said signal providing means including means for converting radiantenergy into energy carried by electronic charges, and said signalproviding means being spaced from said distributing means to permitquanta of radiant energy emanating from points disposed at differntangular orientations to said signal providing means to impinge upon acommon point of said signal providing means.

39. The combination according to claim 38 further comprising meanscoupled to said signal providing means for storing said signals, andmeans for focussing said signal providing means.

40. The combination according to claim 39 further comprising means forextracting data from said storage means, said extracting means includingmeans for filtering said data, said filtering means having a filtercharacteristic complementary to said spatial distribution.

41. In combination:

means responsive to a spatial distribution of quanta of radiant energyfor providing a transform domain representation of an image, said meansproviding signals having data relative to the locations of said quantaradiant energy and including means for converting radiant energy intoenergy carried by electronic charges suitable for electronicamplification; and

means responsive to said signals for decoding said spatial distributionto extract data from said signals, said data being suitable for formingan image.

42. The combination according to claim 41 further comprising means forstoring said signals.

43. The combination according to claim 42 further comprising means forextracting data from said storage means, said extracting means includingmeans for filtering said data, said filtering means having a filtercharacteristic complementary to said spatial distribution, and means forscanning said signal providing means.

\ UNIT D STATES PATENT OFFICE CERTEFEQATE 0F CURREQTION Patent No.3,748,470 WW Dated July 24, 1973 lnventor(s) Harrison H. Barrett It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column 1, line 34, after "pro'v'icles insert a system v Column 1, line52, change marks to mask Column 3, line 27, change "edge" to imageColumn 4, line 22, change "wit" to with Column 4, line 34; change"travls" to travels Column 4, line 56, change "prowlie to provide Column5, line 23, after "to" insert the after "form" insert of Column 5, line33 after "of" insert a Column 6, line fSl change "te to the Column 6,line 65, delete "05 {second occurrence) and after "and" insert of Column8, line45, change "wile to while Column 8, line 52, changecondiguration" to configuration Column 9;, line 1, change "95" to 97Column 9, line 22, change "at" to by Column 9, line 54 change which." toeach FORM po'wso uscoMM-oc 60376-P69 U.S. GOVERNMENT PRINTING O'I'ICE I9', DJ5-J3l 1 l i y I J' NITE D sTATEs PATENT OFFICE 4 Page 2 gCERTIFICATE OF CORRECTION PatentNo. 31748,47Q H Datmi July 24,-1973Inventor( Harrison i1. Barrett 1 It is certified that error appears inthe above-identified patent gand that said Letters Patent are herebycorrected as shown below:

Column 10, line 21, change "the" (second occurrence) to The 'r I 1 I 7Column 11, line 9, change "therby" to thereby Column 12, line 28; change"characteristic" to characteristic Column 16, line 43; change "cathod"to cathode Column 16, line 60, after "while" insert in Column 17, line55; Claim 1; delete "siad".

Column 21, line 9, Claim 17, after "ject," insert said correlating meanscomprising frequency dispersive filtering means, 1-

Column 22, line 38, Claim 22, change "charactertistic" to characteristicColumn 22, line 41, Claim 22, change "filter" (first occurrence) tofiltered Column 25, line 22, Claim 38; change "differnt" to different--Column 26, line 12 Claim 41, after "quanta" insert of Signed and sealedthis 1st day of October 1974.

(DEAL) ttest GIBSON JR. AL DANN Arresting Officer 4 Y I CommissionerlofPatents Foam eo-wsono-es) v l uscoMM-DC 00376-P69

1. In combination: means for spatially distributing sequentiallyoccurring quanta of radiant energy in a coded format, said distributionhaving a succession of first regions and a succession of second regions,the transmissivity of said second regions to said raDiant energy beingless than the transmissivity of said first regions to said radiantenergy, said first regions being interspersed among said second regionsand being arranged in accordance with said format; means responsive tosaid quanta of radiant energy for providing signals having informationrelative to the locations of said quanta of radiant energy, said signalproviding means including means for converting radiant energy intoenergy carried by electronic charges; said signal providing means beingspaced apart from said distributing means such that quanta of radiantenergy emanating from loci which are spaced apart and equidistant fromsiad said distributing means can impinge upon a single point of saidsignal providing means; and means having information relative to saidformat for decoding said signals to extract therefrom informationrelative to locations of points of emanation of said quanta of radiantenergy.
 2. The device as defined by claim 1 wherein said decoding meansprovides an image and comprises: means for scanning the information ofsaid signals, said scanning means providing a time modulated signal inresponse to the locations of said quanta; and means for filtering saidtime modulated signal to provide a point of said image.
 3. The device asdefined by claim 2 further comprising: means responsive to saidfiltering means for displaying said point of said image; and means forcoordinating said display means with said scanning for positioning saidpoint within said image.
 4. In combination: means responsive to quantaof radiant energy emitted sequentially from a source of such radiantenergy, said means inhibiting the passage of such ones of said quantabeing emitted in any one of a plurality of predetermined directions,said means permitting the passage of at least some of said quanta ofradiant energy emitted from said source in other predetermineddirections, said means being further structured for providing a sequenceof regions of inhibited passage and a sequence of regions of permittedpassage of quanta of radiant energy, said regions of inhibited passageand permitted passage varying in size in accordance with a predeterminedspatial code; means including scintillation means for detecting thepresence of such ones of said quanta of radiant energy which have passedthrough said impeding means, said detecting means providing signalshaving information relative to the locations of such quanta; saiddetecting means and said inhibiting means being positioned relative toeach other and relative to said source such that quanta of radiantenergy emitted from separate points of said source and passing throughseparate ones of said regions of permitted passage can impinge upon asingle point of said detecting means; and means responsive to saidsignals of said detector means for decoding said information to providean image of said source of radiation.
 5. In combination: means forilluminating an object with quanta of radiant energy, said means havingregions of emission of said radiant energy interspersed among regions ofnon-emission, said regions of emission being arranged in a spatiallycoded pattern, said means being positioned relative to said object topermit quanta of radiant energy from different ones of said emissiveregions to impinge upon a single point of said object; means responsiveto the transmissivity of said object to said radiant energy fordetecting radiant energy transmitted through said object, said detectingmeans providing information relative to the locations of such ones ofsaid quanta of radiant energy arriving at said detecting means within apredetermined interval of time; and means responsive to said informationof said detecting means for decoding said spatially coded pattern toprovide an image of said object.
 6. In combination: means responsive torays of radiation emitted from an object having sources of suchradiation for moduLating said radiation while retaining the directionsof said rays, said means comprising an array of radiation transmissiveregions interspersed among relatively opaque regions, said transmissiveregions being arranged in accordance with a predetermined format; meansfor detecting said modulated radiation, said detecting means beingpositioned relative to said modulating means such that one of said raysof radiation transmitted via one of said transmissive regions and asecond of said rays of radiation transmitted via a second of saidtransmission regions can impinge upon a single point of said detectingmeans, said detecting means providing a signal having informationrelative to said format and to the locations of such ones of said raysof radiation which pass through said transmissive regions; and means forcorrelating said first signal with the arrangement of said transmissiveregions in said predetermined format to provide an image of said object,said correlating means including means for scanning said detector signaland means for filtering the output of said scanning means, saidfiltering means being frequency dispersive.
 7. The device defined byclaim 6 wherein said correlating means further comprises: means forgenerating a second signal which is modulated with said informationrelative to said format and further modulated with said informationrelative to said rays of radiation; and second means for providing afiltering function and filtering said detector signal, said secondfiltering means having a temporal weighting function complementary tothe arrangement of said transmissive regions in said format forproviding an image of said object.
 8. In combination: means responsiveto the energy of particles moving along substantially linear paths formodulating the intensity of said particles, said modulating meanscomprising an array of barrier elements having predetermined sizes andbeing arranged in a predetermined format; means for detecting selectedones of said particles which pass between said barrier elements toprovide a signal having information relating to the locations of saidselected particles, said detecting means being spaced from saidmodulating means to permit particles moving along a pair of said pathsdisposed on opposite sides of a barrier element to impinge on a singlepoint of said detector means; and means for comparing said signal withsaid format to extract said information for forming an image.
 9. Animaging system responsive to radiation emitted from an object, saidimaging system comprising: means for spatially modulating said radiationwhile retaining the direction of rays of said radiation, said moduatingmeans comprising an array of radiation transmissive regions havingdiffering sizes and arranged in a predetermined configuration; meansresponsive to said spatially modulated radiation for forming a firstimage having information relative to said object and relative to saidpredetermined configuration, said first image forming means beingpositioned relative to said modulating means such that one of said rayspassing through one of said transmissive regions and a second of saidrays passing through a second of said transmissive regions can impingeupon a single point of said first imaging forming means; a delay medium;and means for transmitting portions of said first image through saiddelay medium, said delay medium imparting to each of said portions adifferential delay complementary to a corresponding portion of saidpredetermined configuration for providing said information relative tosaid object.
 10. The system as defined by claim 9 further comprisingmeans responsive to said transmission means for displaying an image ofsaid object.
 11. The system as defined by claim 10 wherein saidtransmission means comprises: means for scanning said first image toprovide a time modulated signal containing information relative to saidpredetermined configuration; and Wherein said delay medium comprisesmeans for generating surface waves.
 12. The system as defined by claim11 wherein said modulating means further comprises means for impedingradiation having an energy lower than a preset magnitude.
 13. An imagingsystem comprising: a source emitting radiation for illuminating anobject, said source being adapted to provide said radiation with aspatially modulated pattern, said source having a series of spaced apartluminous regions each of which is positioned for illuminating a commonpoint on said object; means responsive to said spatially modulatedradiation for forming a first image having information relative to saidobject and relative to said pattern; a delay medium; and means fortransmitting portions of said first image through said delay medium,said delay medium imparting to each of said portions a differentialdelay inverse to a corresponding portion of said pattern for providngsaid information relative to said object.
 14. The system as defined byclaim 13 further comprising means responsive to said transmission meansfor displaying an image of said object.
 15. The system as defined byclaim 14 wherein said transmission means comprises: means for scanningsaid first image to provide a time modulated signal containinginformation relative to said pattern; and wherein said delay mediumcomprises means for generating surface waves.
 16. An array of regionseach of which comprises a radiation emissive material and has apredetermined size, each of said regions being spaced apart such thateach of said sizes and each of said spacings have preselected magnitudesfor providing a predetermined spatial frequency characteristic, andmeans for positioning each of said regions in said array, a plurality ofregions of said array of regions being arranged in a sequence accordingto the magnitudes of their sizes and their spacings ordered bymonotonically increasing magnitudes to provide said spacial frequencycharacteristic with a characteristic of a chirp wave form.
 17. Incombination: means responsive to rays of radiation emitted from anobject having sources of such radiation for modulating said radiationwith a spatial pattern while retaining the directions of said rays, saidmeans comprising an array of radiation transmissive regions illuminatedby said radiation and interspersed among relatively opaque regions, saidtransmissive regions being configured and arranged in accordance with apredetermined format such that said spatial pattern contains informationrelative to said format; and means responsive to the locations of saidmodulated rays of radiation for correlating said modulated rays withsaid format to derive an image of said object, said correlating meansbeing positioned relative to said modulating means such that one of saidrays passing through one of said transmissive regions and a second ofsaid rays passing through a second of said transmissive regions canimpinge upon a single point of said correlating means.
 18. The device asdefined by claim 17 wherein said correlating means comprises means forvarying said responsivity in accordance with the spacing between saidobject and said modulating means whereby said device is focused.
 19. Incombination: means responsive to rays of radiation emitted from a sourceof radiation for modulating said radiation, said means comprising anarray of radiation transmissive regions interpersed among relativelyopaque regions, said transmissive regions being arranged in accordancewith a predetermined format; means including scintillation means fordetecting said modulated radiation for providing a signal havinginformation relative to said format and to the locations of such ones ofsaid rays of radiation which pass through said transmissive regions;said detecting means being spaced apart from said modulating means topermit rays of radiation passing through noncontiguous ones of saidtransmissivE regions to impinge upon a common point of said detectingmeans; and means for correlating said signal with said predeterminedformat to provide the direction of said source.
 20. In combination:means responsive to the energy of particles emanating from a source ofsuch particles and moving along substantially linear paths formodulating the energy of said particles, said modulating meanscomprising an array of barrier elements having predetermined sizes andbeing arranged in a predetermined format; means for detecting selectedones of said particles which pass between said barrier elements toprovide a signal having information relating to the locations of saidselected particles, said barrier elements being spaced from saiddetecting means to permit particles traveling on opposite sides of oneof said barrier elements to impinge upon a common point of saiddetecting means; and means for comparing said signal with said format toextract said information to provide the direction of said source.
 21. Incombination: means for modulating the spatial distribution of quanta ofradiant energy illuminating an object, said spatial modulation having apredetermined format; means responsive to the locations of quanta ofradiant energy for receiving said quanta of radiant energy, saidreceiving means preserving information relative to said locations; andmeans for filtering said received radiant energy concurrently with thereception of quanta of radiant energy by said receiving means, theimpulse response function of said filtering means having a formatcomplementary to said spatial modulation format for providinginformation relative to said object.
 22. A scanning system comprising:means for modulating the distribution of radiant energy emanating froman object, said modulating means having a succession of radiationtransmissive regions of differing sizes, said radiation transmissiveregions being arranged in a sequence of monotonically increasing sizesin a first direction and in a second direction; means for detecting saidquanta of radiant energy, said detecting means providing an electricalimpulse in response to the reception of a quanta of said radiant energy,said detecting means being spaced apart from said modulating means topermit radiant energy passing through different ones of saidtransmissive regions to impinge upon a common point of said detectingmeans; means for storing said impulses, said storage means preservingdata relative to the locations of the received quanta of radiant energy;means for filtering the data in said storage means, said filtering meanshaving a phase characteristic which is the inverse of the spatialmodulation format of one of said sequences of transmissive regions;second storage means for receiving data from the filtering means; secondfiltering means for filtering the data in said second storage means,said second filtering means having a phase charactertistic which isinverse to that sequence of said transmissive regions in a seconddirection; and means responsive to the data filter by said firstfiltering means and the data filtered by said second filtering means forproviding image points of said object in a first direction and in asecond direction.
 23. The scanning system of claim 22 wherein said firstfiltering means includes means for scanning said first storage means inaccordance with a predetermined format.
 24. The scanning system inaccordance with claim 23 wherein said filtering means comprises asurface wave delay line.
 25. The scanning system in accordance withclaim 24 wherein said first storage means comprises a storage tubedisplay.
 26. The scanning system in accordance with claim 25 whereinsaid scanning of said first storage means provides a chirped frequencysignal to said first filtering means.
 27. A scanning system comprising:means for placing a source of radiant energy in an object to be scanned;means for detectIng said radiant energy; means interposed between saidobject and said detecting means for casting a shadow of said radiantenergy upon said detecting means, said shadow comprising a plurality ofshaded regions varying in size and position in accordance with apredetermined format; said shadow casting means being spaced from saiddetecting means such that a second source of radiant energy locatedalongside the aforesaid source of radiant energy casts a second shadowcomprising a plurality of shaded regions which overlap the shadedregions of the aforesaid shadow; means coupled to said detecting meansfor storing data relative to the configuration of said shadow; and meansfor processing said stored data while said radiant energy is incidentupon said detecting means, said processing means providing data relativeto the form of said object.
 28. In combination: an array of sources ofradiant energy positioned to illuminate an object, said sources havingdiffering sizes and being arranged in a predetermined format; means fordetecting quanta of said radiant energy, said detecting means beingpositioned relative to said object such that radiant energy from aplurality of said sources can impinge upon a common point of said objectand in passing by said object is incident upon said detecting means,said detecting means providing data relative to the spatial positions ofsuch ones of said quanta of radiant energy which are incident upon saiddetecting means; and means for filtering the data provided by saiddetecting means, said filtering means having a phase characteristicfunctionally dependent upon said format to provide data relative to theform of said object.
 29. In combination: means for altering the spatialdistribution of gamma rays, said gamma rays being utilized forilluminating an object, said altering means comprising a succession ofradiation transmissive regions dispersed among regions of relativeopacity to gamma rays, said transmissive regions being arranged in apredetermined format, said transmissive regions having a depth smallerthan the width of such regions; means for detecting such ones of saidgamma rays that pass through said altering means, said detecting meansproviding data relative to the locations of said gamma rays; and meansfor correlating said data with said format to provide information aboutsaid object.
 30. A nuclear imaging system comprising: means for alteringthe spatial distribution of radiation utilized for illuminating anobject, said altering means comprising a succession of radiationtransmissive regions interspersed among regions of relative opacity tosaid radiation, said transmissive regions being arranged in apredetermined format in the form of a chirp pattern in at least onedimension such that the transmissive regions are arranged according tosize in a monotonically decreasing array; means for detecting rays ofsaid radiation that pass through said altering means, said detectingmeans including means for providing data relative to the locations uponsaid detecting means where individual rays of said radiation impinge;and means for correlating said data with said format to provideinformation about said object.
 31. The nuclear imaging system inaccordance with claim 30 wherein the format of said altering meansincludes a chirp pattern in a second dimension providing an array ofradiation transmissive regions arranged according to size in amonotonically decreasing array.
 32. The nuclear imaging system inaccordance with claim 31 wherein: the detecting means further comprisesmeans for storing said data, said data being stored in the form of anarray of points each of which represents the location of a point ofimpingement of a ray of radiation upon the detecting means; and whereinsaid correlating means comprises means for scanning the array of datapoints of said detecting means to provide a scan signal, saidcorrelating means further coMprising means for filtering said scansignal, the frequency bandwidth of said scan signal being related to thespacing between locations of said points of impingement of rays ofradiation upon said detecting means, said filtering means enabling afocussing of said nuclear imaging system when the bandwidth of said scansignal approximates the bandwidth of said filtering means.
 33. Theimaging system in accordance with claim 32 further comprising means forvarying said focus.
 34. The imaging system according to claim 33 whereinsaid variable focus means comprises means for varying the scanning rateof said scanning means of said correlating means.
 35. A nuclear imagingsystem comprising: means for illuminating an object with radiation, saidilluminating means comprising a succession of radiation emissive regionsinterspersed among regions of non-emission, said emissive regions beingarranged in a predetermined format in the form of a chirp pattern in atleast one dimension such that the emissive regions are arrangedaccording to size in a monotonically decreasing array; means fordetecting rays of said radiation that pass from said illuminating means,said detecting means including means for providing data relative to thelocations upon said detecting means where individual rays of saidradiation impinge; and means for correlating said data with said formatto provide information about said object.
 36. The nuclear imaging systemin accordance with claim 35 wherein the format of said illuminatingmeans includes a chirp pattern in a second dimension providing an arrayof radiation emissive regions arranged according to size in amonotonically decreasing array.
 37. The nuclear imaging system inaccordance with claim 36 wherein: the detecting means further comprisesmeans for storing said data, said data being stored in the form of anarray of points, each of which represents the location of a point ofimpingement of a ray of said radiation upon the detecting means; andwherein said correlating means comprises means for scanning the array ofdata points of said detecting means to provide a scan signal, saidcorrelating means further comprising means for filtering said scansignal, the frequency bandwidth of said scan signal being related to thespacing between locations of said points of impingement of rays of saidradiation upon said detecting means, said filtering means enabling afocussing of said nuclear imaging system when the bandwidth of said scansignal approximates the bandwidth of said filtering means; and whereinsaid nuclear imaging system further comprises means for varying saidfocus, said variable focus means comprising means for varying thescanning rate of said scanning means of said correlating means.
 38. Incombination: means for spatially distributing quanta of radiant energyin a coded format, said distribution having a succession of regions ofdiffering dimensions, said regions having differing amounts of saidquanta; and means responsive to said quanta of radiant energy forproviding signals having data relative to the locations of said quantaof radiant energy, said signal providing means including means forconverting radiant energy into energy carried by electronic charges, andsaid signal providing means being spaced from said distributing means topermit quanta of radiant energy emanating from points disposed atdiffernt angular orientations to said signal providing means to impingeupon a common point of said signal providing means.
 39. The combinationaccording to claim 38 further comprising means coupled to said signalproviding means for storing said signals, and means for focussing saidsignal providing means.
 40. The combination according to claim 39further comprising means for extracting data from said storage means,said extracting means including means for filtering said data, saidfiltering means having a filter characteristic complementary to saidspatial distribution.
 41. IN combination: means responsive to a spatialdistribution of quanta of radiant energy for providing a transformdomain representation of an image, said means providing signals havingdata relative to the locations of said quanta radiant energy andincluding means for converting radiant energy into energy carried byelectronic charges suitable for electronic amplification; and meansresponsive to said signals for decoding said spatial distribution toextract data from said signals, said data being suitable for forming animage.
 42. The combination according to claim 41 further comprisingmeans for storing said signals.
 43. The combination according to claim42 further comprising means for extracting data from said storage means,said extracting means including means for filtering said data, saidfiltering means having a filter characteristic complementary to saidspatial distribution, and means for scanning said signal providingmeans.